Your eyes are one of the most complex organs in your body. A comprehensive eye exam to assess your visual system and eye health involves a number of different of tests. Unlike a simple vision screening, which only assesses your vision, a comprehensive eye exam includes a battery of tests in order to do a complete evaluation of the health of your eyes and your vision.
The tests that you will undergo in a comprehensive eye examination may vary from eye doctor to eye doctor but here are are some common exams that you may encounter:
Patient Background and History
One of the most important parts in a comprehensive eye exam is your patient health history. This information will alert your doctor to any conditions that should be monitored closely, such as an allergy to any medications, current or family history of systemic or eye pathology or environmental conditions that could be affecting your vision or eye health.
This will also help your doctor to determine any preventative eye care measures that are relevant to keep your eyes healthy for years to come.
Visual acuity is a measurement of your vision using an eye chart, the Snellen Eye Chart. In this test the patient is seated at a standard distance and is asked to read letters or symbols of various sizes, which get smaller as you move down the chart.
The results are the familiar ratio of 20/20, 20/40 etc. which is a comparison of your vision compared to the average person with good vision, which is typically 20/20.
For example, a patient that has 20/40 vision, can only see at 20 feet what the normal person can see from a distance of 40 feet. This test is a preliminary test of how clearly you are seeing in each eye but it does not give you a prescription for corrective lenses.
Those who don’t have 20/20 vision have what is referred to in most cases as a “Refractive Error.” The patient may have nearsightedness, farsightedness, astigmatism or other eye conditions that prevent the patient from seeing 20/20. A refraction will tell the doctor which prescription lenses will correct your eyesight to achieve 20/20 vision or whichever amount your vision is correctable to.
A refraction may include a couple of steps.
Retinoscopy is a test that allows the doctor to obtain an approximate prescription for eyeglasses. In this test the doctor uses a hand-held instrument called a retinoscope that shines a light into the patient’s eye. The doctor then analyzes the reflex of the light from the patient’s eye to determine the patient’s prescription for glasses.
An instrument called a phoropter is something most patients associate with an eye exam. This space age appearing instrument, positioned in front of the patient’s face during the eye exam, gives the doctor the ability to determine the patient’s focusing ability as well as their eye alignment. The phoropter also determines which, out of the hundreds and hundreds of potential eyeglass prescriptions, will help the patient see as clear as possible. Using the phoropter, the doctor will ask the patient which series of lenses makes their vision the clearest.
While retinoscopy is quite effective for children and nonverbal patients, there are now a number of computerized or automated instruments available today to help doctors accurately determine a patient’s eyeglass prescription.
Autorefractors and Aberrometers
Autorefractors and aberrometers are computerized machines that are able to measure your refractive error to determine your prescription for glasses or contact lenses. These instruments are usually used in addition to testing described earlier:
– An autorefractor is similar to retinoscopy, which electronically analyses the light reflex from the patient’s eye.
– An aberrometer measures distortions or aberrations in the cornea and lens of the eye that disrupt proper focus of light on the retina. Using wavefront technology, the instrument measures the rays of light as they pass through your eye to look for imperfections which may indicate a refractive error.
During the comprehensive eye exam, your eye doctor will also want to test how your eyes function individually and together from a mechanical perspective. In order to see clearly and comfortably, your eyes need to work together as a team.
The final and most important aspect of a comprehensive eye exam is a check of your overall eye health. These tests (below) are done to identify any eye conditions or diseases, both inside the eye as well as the external parts of the eye, that could affect your vision and general health.
Slit Lamp Test
The slit lamp or biomicroscope is an instrument that allows the doctor to examine the internal and external parts of the eye in detail, such as the conjunctiva, iris, lens, cornea, retina and the optic nerve. The patient rests their forehead and chin on a headrest to stabilize the head, while the doctor looks into the eye with the slit lamp microscope, which is magnified with a high-intensity light. A slit lamp test enables the doctor to evaluate the eyes for signs of normal aging and eye pathology, such as conjunctivitis, cataracts, macular degeneration or retinal detachment. Early diagnosis and treatment of eye diseases are essential for preventing vision loss.
Tonometry is a test to detect glaucoma by measuring the pressure inside your eye or IOP (intraocular pressure). Glaucoma can cause vision loss and even blindness if the IOP in the eye is too high and damages the optic nerve.
The applanation tonometer, typically attached to a slit lamp, is one of the most common instruments used to measure the pressure in the eye. Prior to doing this test the doctor will numb the patient’s eyes using an anesthetic, before gently applanating (putting pressure on) the patient’s cornea to measure the pressure in the eye.
During your comprehensive eye exam, your doctor may decide to do a dilated eye exam. In this test, your doctor will instill dilating drops in each eye, which would enlarge your pupils to give the doctor a better view of certain parts of the back of the eye. Dilation is done at the discretion of the doctor, with some patients dilated every year and others at specified intervals; the frequency of dilation will vary for each patient.
Typically the drops take around 20 to 30 minutes to take effect and may last up to several hours following the exam; each patient is different. Since more light enters your eyes when your pupils are dilated, you will be more sensitive to bright light, especially sunlight. Although your doctor may provide disposable sunglasses, you may want to bring a pair of sunglasses to wear after the exam to make it more comfortable until the drops wear off.
A comprehensive eye exam is an important part of your overall general health maintenance and should be scheduled on a regular basis. The findings from your comprehensive eye exam can give your doctor important information about your overall health, particularly diabetes and high blood pressure.